This invention relates to high intensity internal mixing machines of the batch type having a mixing chamber shaped to accommodate two counter-rotating non-intermeshing winged rotors. The batch of ingredients to be mixed into a homogeneous mass is fed down into the mixing chamber through a vertical chute and is pushed down under pressure by a ram located in the chute. This ram is hydraulically or pneumatically driven. The lower face of the ram, when advanced down to its operating position during mixing of the batch, forms an upper portion of the mixing chamber. The homogeneous mixture produced is removed from the mixing chamber through a discharge opening at the bottom of the chamber, and a door associated with this opening is then closed in readiness for the next batch of ingredients to be introduced down through the chute.
Some internal batch mixing machines are designed with non-intermeshing rotors, and others have intermeshing rotors. Intermeshing rotors must always be driven at the same rotational speed in synchronized relationship; non-intermeshing rotors may be driven at the same rotational speed or at different rotational speeds for achieving different mixing an kneading effects. The present invention relates to the non-intermeshing type. The wings of the rotors have a generally helical configuration, and they produce high intensity mixing and homogenization by the co-operative interaction of their various forceful dynamic effects, as described later. For further information about such internal batch mixers, having non-intermeshing rotors, reference may be made to U.S. Pat. Nos. 1,200,070 and 3,610,585, assigned to predecessors of the present assignees and to recent U.S. Pat. No. 4,714,350, in my name as inventor, and the disclosures of these patents are incorporated herein by reference as background information.
The vast majority, probably more than ninety-five percent (95%), of all internal batch mixing machines in commercial usage today in the United States having non-intermeshing rotors are operated non-synchronously, i.e. with the rotors being driven at different rotational speeds, often called "friction ratio" operating mode. For example, a typical non-synchronous operation causes one rotor to make 9 revolutions versus 8 revolutions for the other rotor, i.e. a "friction ratio" of 9 to 8 or 1.125 to 1.
In U.S. Pat. No. 4,714,350 are described novel two-wing, non-intermeshing rotors of increased performance adapted for either non-synchronous or synchronous operation. Thus, those two-wing rotors may be retrofitted into existing non-synchronous internal batch mixers which currently comprise the overwhelming majority of batch mixers and also may be employed to advantage in synchronous batch mixers.
In U.S. patent application Ser. No. 918,155, filed Oct. 14, 1986, now U.S. Pat. No. 4,744,668, issued May 17, 1988, in my name as inventor, are described novel four-wing and three-wing rotors of increased performance adapted for use in either the currently more numerous non-synchronous batch mixers or synchronous bach mixers.
In both U.S. Pat. No. 4,714,350 and in the patent application, there is a recognition that optimum or preferred results are achieved by driving the specified rotors synchronously while oriented in a preferred phase angle relationship. The patent specifies that preferred phase angle relationship as being about 180.degree.. Further experimentation and testing has confirmed that synchronous operation at a phase angle relation of 180.degree. is indeed an optimum operating procedure for non-intermeshing internal batch mixers, and the present novel rotors have been conceived and developed to yield optimum results for rubber and plastic mixing in internal batch mixing machines driven synchronously at the optimum phase angle of 180.degree.. In view of the fact that the vast majority of internal batch mixers in commercial usage are now driven non-synchronously, this invention indicates that retrofitting such machines for synchronous operation is likely to be rewarding in many instances.